96 S-10 Fuel Sender Issue

[wickedude]

My fuel pump went bad on my 2.2 96 S-10 so I bought and installed a AC Delco MU1781 which is supposed to be the newer style pump for this application. It came with a new pigtail connector which I spliced into my vehicle harness.

So I install the pump, everything works great. Then I go to fill up the tank with 18 gallons of fuel and my dash gauge is only at about 3/4 fuel. It will not go up to half. I thought it was kinda strange when I poured in 5 gallons initially and I was barely off of empty.

So I took the pump back out and when the float is flat I get 1.5 ohms resistance. At the full position its about 90 ohms. Is this the correct range for the s-10? My Alldata subscription does not give ohm values for the sending unit. Can any one chime in or have other had issues with the MU1781? Thanks!

[aleekat]

Someone will correct me if wrong but I believe the range is 0-90. When you had it out, did you turn the key on and move the float full range and see if the gauge acted properly? I do know there is a "buffer" to keep the gauge from bouncing all around with less that full. It's also possible your float has a pin hole and the fuel in trapped inside the float. I've had this happen on a couple vehicles.

[wickedude]

This is the weirdest thing I have seen for awhile now. I pulled the pump out and checked the float. Everything was correct. 90 ohms at full, 1.5 at empty. Old pump put out about 96 ohms when full. Is that enough of a difference for an 1/8th of the tank?

Yeah now like an idiot I wish I plugged in just the pump and see what the gauge read. Where is this buffer? The gauge is moving around a lot I noticed even when full. Im wondering now if there is a gauge issue....

[aleekat]

http://www.s10forum.com/forum/f105/i...d-this-347914/
I'm not sure of the location. But it sure looks like lots of S10 fuel level issues.

[wickedude]

Wow I never even heard of a fuel buffer. Its not in my alldata info either. Sure sounds like the issue though. Im going to hunt around the glove box today to see if I can find it. Thanks man!

[aleekat]

You may want to post over at that other board. It seems lots of them have the issue. Post back, I'll be curious if that is the issue. I know most fuel indicating symptoms have some type of buffer or compensation.

[wickedude]

So after looking all over I can find no fuel buffer on my 96. It appears to be a 97 only part based off other posts I read. I test the purple signal wire coming off the pump and it only is about 72 ohms with the tank full. Should be about 90. I put a 10 ohm resistor in and sure enough my fuel gauge now reads full. So for whatever reason my fuel sender is not sending a full 90 ohms on a fuel tank though I know the sender was when I tested it out of the tank. Im thinking now its a issue with the float. The float on this new module was like half the size of the old.

[j cAT]

the pump you got a mu1781 is the correct one, the delphi pump FG 0027 is the other pump I would use.

if the old pump read 90 ohms then the new pump should also. try another pump and measure at the store to see if you purchased the correct pump or was made defective.

also make sure that the pump says on it mu1781 !

[wickedude]

The pump is indeed a MU1781. It worked correctly out of the tank, perfect 90 ohms when holding the float full up. The issue is why its not working correctly in the tank. Im leaning towards the smaller float is bad. When I burn off some gas I either replace the float or retro fit my old float onto the rod im thinking.

[j cAT]

Originally Posted by wickedude

The pump is indeed a MU1781. It worked correctly out of the tank, perfect 90 ohms when holding the float full up. The issue is why its not working correctly in the tank. Im leaning towards the smaller float is bad. When I burn off some gas I either replace the float or retro fit my old float onto the rod im thinking.

I did not find any issues with this pump . maybe its a chinese clone.

where did you purchase this pump ? COST$$$.